Planetary ball mill



June 6, 1933. .1. CRITES PLANETARY BALL MILL Filed Oct. 9, 1930 5 Sheets-Sheet l Imfenfi)? Joe 0122s 1 5 June 6, 1933. J. CRITES PLANETARY BALL M ILL Filed Oct. 9, 1930 5 Sheets-Sheet 2 I Imfenm (70 9 it-2 25? June 6,1933. R E 1,912,761

PLANETARY BALL MILL Filed Oct. 9, 1950 s Sheets-Sheet 5 June 6, 1933. J. CRITES PLANETARY BALL MILL Filed Oct. 9, 1930 5 Sheets-Sheet 5 wig gl n Passes J n; 6, 1 33 UNITED- STATES PATENT OFFICE J01!"- CRITES, OF NEW YORK, N. Y., ASSIGNOR TO THE RAYMOND BROTHERS IMPACT PULVERIZEB 00., OE CHICAGO,

ILLINOIS, A CORPORATION or 'ILLmoIs PLANETARY BALL MILL Application filed October 9, 1930. Serial No. 487,522.

This invention relates to certain new and useful improvements in planetary ball mills of the type in which an annular series of grinding balls is caused to revolve about a central vertical axis between relatively movable ball races or grinding rings.

Briefly described, the improved grinding mill comprises a closed housing in the lower portion of which are mounted the grinding elements consisting of an annular series of grinding balls adapted to revolve about a vertical axis, and a plurality of relatively movable grinding rings centered about this vertical axis and between which the balls are confined. A central vertical driven shaft serves to support and rotate one or more of the grinding rings. Means are provided for feeding material to be ground or pulverized into the upper or intermediate portion of the housing so thatthe material will fall by gravity between the grinding elements. A circular series of plows are supported and rotated by the central driven shaft beneath the grinding elements to lift unpulverized material from the lower portion of the housing and project same upwardly between or over the'grinding elements. An upward circulation of air is maintained through the houstype hereinabove referred to,

ing. to carry away in suspension the pulver ized material.

The general object of this invention is to provide an improved mill construction ofthe type briefly described hereinabove and disclosed more in detail in the specifications which follow.

Another object is to provide, in combination with planetary grinding elements of the improved means to project material to be ground upwardly between or above the grinding elements.

Another object is to provide, in combination with grinding elements ofthe type hereinabove referred to, .a

grinding rings on the balls.

Other objects and advantages of this in plurality of rotary plows for lifting material from the lower portion of the housing and throwing same upwardly into position to be ground.

Another object is to provide improved means for distributing the unpulverized materialwhich is projected upwardly so that part will pass upwardly between the grinding elements and part will be carried above the grinding elements.

Another object is to provide improved means for yieldingly holding the grinding rings or races in yielding engagement with the balls. 7

Another object is to provide improved means for adjusting the pressure of the vention will be more apparent from the following detailed description of certain ap proved forms of'apparatus built according to the principles of this invention.

In the accompanying drawings:

Fig. 1 is a general elevation of a grinding asseimbly in which a mill of. this type may be use Fig. 2 is a central verticalsectionthrough one formof the mill.

Fig. 3 is a horizontal section, taken substantially on the line 3-3 of Fig. 2.

Fig. 4 is a perspective view of the assembled inner grinding rings orfraces shown in Fig. 2.

Fig. 5 is a perspective view of the lower inner grinding ring as seen from below.

Fig. 6 is a side elevation of the grinding ring assembly shown in Fig. 4, with parts broken away.

Fig. 7 is a horizontal section taken substantially on the line 77 of Fig. 2. 1

Fig. 8 is a perspective view of one of the plows.

to Fig. 2, showing a modified form of mill.

stantially on the line 10-10 of Fig. 9.

Fig. 9 is a central verticalsection, similar provided for feeding material to be ground or'pulverized into the housing 1 above the grinding elements. A feeder of a well-known type is here shown comprising a slide valve 4 and a rotary pocket feeder v5 which is driven at an adjustable speed by means of a suitable mechanism indicated generally at 6 so as to regulate the rate of feed of the-material into the mill. A fan indicated generally at 7 serves to draw air from the mill housing 1 through the pipe or conduit 8 thus carrying away finely pulverized material in suspension. This air and suspended material .is projected from the fan casing through pipe or conduit 9 into the cyclone separator indicated at 10.- Most of the suspended pulver-- ized material here separates out and is collected in a suitable receiver 11. The air flows back from separator 10 through conduit 12 into the air chamber or manifold 13 which encloses the lower portion of the mill housing, the air flowing inwardlv through passages 14 and thence upwardly between the grinding elements, hereinafter described, so as to carry away more of the pulverized material through the outlet conduit 8. The rotary elements of the mill and the fan 7 may be driven in any suitable manner. As shown in Fig. 1, these elements are connected by a belt gearing with a driving counter-shaft 15. A grinding and separating system of the type briefly described hereinabove is old and well known with other types of mills.

Referring now more particularly to Figs. 2 to 8 inclusive, the main lower casting or supporting frame 16 comprises a base plate 17 supported on the pedestal 2 and an upper supporting ring 18 connected with base plate 17 by an annular series of posts 18 between which are the air inlet ports 14. The air chamber or manifold 13, which may be constructed of suitable sheet material, is supported by and secured to the base plate 17 and supporting ring 18, as indicated at 19 and 20, respectively. Preferably this inanifold 13 is formed with a spiral outer wall 21 with its largest portion adjacent the air inlet conduit 12, so that an equal air pressure will be maintained at all points around the mill so that the air will How in equally through the various ports 14.

The main upper mill housing 1 has a flared lower skirt portion 23 which is mounted upon and secured to the supporting ring 18, as by means of the nuts and bolts indicated at 24. The upper wall 25 of air manifold 13 may be secured in place by being clamped between the skirt 23 and supporting ring 18. At an intermediate height in one side of housing 1 is the inlet port 3 with which the material feeder 3 is connected. A removablemanhole cover 26 in one side of housing 1 permits access to the interior of the mill. A roof or cover member 27 closes the upper end of housing 1 and connects with the outlet conduit 8.

A diametrically extending cross-bar 28 formed within the housing 1 at an intermediate height is formed with an annular central portion 29 in which is supported the bearing 30 for the journal 31 at the upper end of the central vertical driving shaft 32. The lubricant chamber for this bearing may be enclosed by an upper cover plate 33 and suitable packing means at the lower end of the bearing is indicated at 34. The journal 35 at the lower end of shaft 32 is rotatably mounted in a bearing sleeve 36 carried by the housin 37 suspended as at 38 from the base plate 1 The housing 37 also carries bearlngs 39 and 40 for a horizontal drive shaft 41 on which is secured beveled pinion 42 meshing with the bevel gear 43 keyed at 44 on the lower portionof vertical drive shaft 32. A suitable roller thrust bearing 45 is interposed between the central collar portion of bevel gear 43 and a portion of housing 37 so as to support the drive shaft 32 and parts carried thereby. A cover plate 46 which serves as a portion of the floor of the pulverizing chamber, closes the top of housing 37 which may-be filled with lubricant for the lower shaft bearings and the bevel driving ears. This lubricant is supplied to houslng 37 through a pipe 47 and flows through port 48 to the bearing surfaces between journal 35 and sleeve 36. The journal 35 may be formed with a spiral groove 49 which assists in carrying this lubricant upwardly between the bearing surfaces.

The outer grinding ring or ball-race 50 has an outer downwardly and inwardly tapered surface 51 adapted to fit within a correspondingly tapered aperture in the supporting ring 18 and beheld in place by clampin screws 52. The outer surfaces of the grinding balls 53 are forced outwardly into enga ement with this outer grinding ring 50. n annular series of these grinding balls 53 will be used, but the number of balls will be insulficient to form a complete circle so that a free space 54 will remain between certain of the balls. During the grinding action of the mill this space 54 may move from place to place between the balls or may be divided Into a series of smaller spaces, the object being to avoid any binding action between the balls and permit a certain amount of space for the material being ground to pass between the balls. In the present form of the inven tion, a pair of inner grinding rings or ball races are used comprising an upper ring 55 and a lower ring 56 provided with ball en-' gaging surfaces which respectively engage the upper and lower portions of the inner sides of each ball 53. Means is provided 7 to yieldingly urge the rings 55 and 56 toward one another at all times. As here shown, a plurality of bolts 57 extend upwardly through mating openings in'the two rings 55 and 56, the bolts having heads 58 which engage the lower sideof lower ring 56. A compression spring 59 surrounding the upper portion of each bolt 57 is confined between the upper side of upper ring 55 and ing ring 50. The pressure exerted by the.

a cap 60 adjustably held in place on the threaded upper end of bolt 57 by means of an adjusting nut 61 and lock nut 62.

It will now be apparent that 'the springs 59 being under compression tend to expand and draw the rings 55 an 56 toward one anotherinto clamping engagement with the inner sides of the balls 53 therebyforcing these balls outwardly against the outer grindinner grinding rings on the balls may be adjusted by varying the tension of springs 59 by means of the adjusting nuts 61. A central hub 63 keyed on an intermediate portion of driving shaft 32 is formed with laterally extending lugs or keys 64 and 65 whichrespectively engage loosel in corresponding recesses formed. in t e respective grinding rings 55 and 56. By this means the inner grinding rings 55 and 56 are rotated with the a shaft 32 but are permitted limited lateral movements to secure proper adjustment against the balls 53 and otherwise centerthe grinding elements without binding.

The intermediate portions of the inner rings 55 and 56, are in the form of spiders formed with annular series of passages 66' and 67 respectively to permit a flow of material through the intermediate portions of these rings. The lower ring 56 is also formed with a plurality of downwardly extending flanges or scoops 68 which project from the rear lower edges of the passages 67 in the direction of rotation of the ring so as to cooperate with the plows hereinafter described in projecting unpulverized material upward 1y through the passages 67 and 66. The lower ring 56 is also formed with a downwardly ta- ,peringor wedge-shaped annular deflecting or flange 69.

rin 1 a l elow the hub 63 there is keyed on shaft 32 the hub 70. of the frame 71 which carries the plows 72, here shown as three in number. Each of theseplows, as shown in Figs.

' 2 and8, is formed with an inner wall 73 by means: of which the plow is secured to the -65 frame 71 and an outer wall 74 for confining which rotates rather c osely adjacent the bottom of the pulverizing chamber. The

plows travel in a. clockwise direction as seen from the top of Fig. 2 so\that the material scooped up by the plows will be thrown upwardly by the inclined bottom wall 76 of each plow. i

The upper face of cover plate 46 is formed with channels 77 and 78 into which project respectively flanges 7 9 and 80 on the lower face of plow frame 71. Oil which is carried upwardl from housing 37 through the bearings of s aft 32 will collect in these channels 77 and 78 and be carried away through drain pipes 81 and 82 respectively. a

In operation, drive shaft 41 will be rotated from any suitable source of power so as to rotate, through beveled gearing 42 and 43,

tion and impart a planetary revolving movement to each of the grinding balls 53, the series of balls traveling around within the outer grinding ring 51 at a speed substantially half that of the inner grinding rings. The plows 72 will simultaneously be revolved about the'central vertical axis along with the inner rings 55 and 56. The material to be ground or pulverized is fed into the housing 1 by means of automatic feeder 3 and falls by gravity upon the grinding elements in the lower portion of the housing. Some of this material will be ground between the engaging surfaces of the balls and rings and some will find its way to the bottom of the housing. The unpulverized material will be picked up by the plows 72 and thrown upwardly. This upwardly projected materlal will be divided by the flange or deflector 69 on the lower ball ring 56, part of the material being deflected upwardly between the balls 53 and the grinding rings, and part of the material being thrown upwardly through the passages 67 and 66 in the inner rings. The scoops 68 hereinabove described assist in throwing this material upwardly through the inner passages. The material which goes upwardly through passages 67 and 66 will be thrown outwardly over the grinding elements and then again fall by gravity between these elements. Air is continually flowing upwardly from the manifold 13 through ports 14 and thence through. the grinding chamber and housing 1 and out through conduit 8. Material which becomes pulverized to a suflicient fineness will be. carried away in suspension in this air stream. The heavier material will continually fallback by gravity Qto the lower portion of the chamber and again be projected upwardly by the plows 72 until ments are held yieldingly in engagement with one another by means of the compressed springs 59. In case metal or other relatively ungrindable material finds its way between the grinding elements, the balls 53 can roll inwardly between the rings 55 and 56 sufliciently to clear these foreign masses, the springs 59 yielding for this purpose. The grinding elements are self-adjusting due both to the flexible driving connections between the shaft 32 and the rings, and the yieldability of the springs 59, so that all shocks are easily absorbed and the mill will'run quietly and efliciently with very small chance of breakage or injury to any of the operating parts.

It will also be seen that the grinding surfaces are self-cleaning, since material tends to flow from between all of these surfaces by gravity and there are no pockets in which either pulverized or unpulverized material may collect.

A different form of the invention is shown in Figs. 9 to 14 inclusive. Features embodied in this mill andrnot specifically described hereinafter may be the same as similar portions of the mill already described and shown in Figs. 1 to 8. Referring now to Figs. 9 to 14, the outer grinding ring 83 is formed with a downwardly and inwardly inclined lower flange 84 formed on its upper face with a ball-race adapted to engage and support the lower outer portions of the balls 53. A single inner grinding ring 85 is formed on its lower outer surface with a ball race adapted to engage the upper inner surfaces of the balls 53. This inner ring 85 is formed with an annular series of passages 86 through which unpulverized material may be projected upwardly from plows 72, and is also formed with a deflecting ring or flange 87 similar to the flange 69 in the first described form of the invention. I

The central vertical driving shaft 88 is of i tubular form, the journal 89 at the lower ehd thereof being rotatably mounted in the bearing 36 as in the first described form of the invention. The closure plate 90 for the top of lubricant housing 37 is formed witha vertical bearing 91 in which an intermediate portion 92 of tubular shaft 88 is journaled. Lubricant from housing 37 which works up through bearing 91 will flow out through a vertical slot 93 and drain pipe 94.

A sleeve or hub 95 is keyed uponthe upper portion 96 of shaft 88, and is formed with a downwardly and outwardly projecting skirt 97 which projects over the hearing 91 and supports the plows 72. Hub 95 is provided with outwardly projecting keys 98 which loosely engage corresponding apertures in the central portion of upper ring 85 so as to impart rotary motion to this'ring while still permitting limited lateral movement of the ring to permit proper centering of the grinding elements.

Since the inner ring 85 rests upon the an-" nular series of balls 83 it may be made of suflicient weight to provide the necessary grinding pressure. However, in the construction here shown, compression springs 99 are provided to yieldably force the upper ring 85 into clamping engagement with the grinding balls. The springs 99 surround guide pins 99 and are confined between the upper face of ring 85 and the lower face of a cap plate 100 secured at 101 to the upper end of a shaft or rod 102 which pro ects downwardly through the centralopening 103 in tubular drive shaft 88. The shaft 102 is formed at its lower end with a flange or collar 104 (Figs. 12 and 14) which engages beneath a ball bearing assembly 105 carried by a cage 106 keyed against rotation at 107 It will now be apparent that by rotating hand wheel 116 ip non-rotary cage 106 may be adjusted up or down within the housing 108, thus imparting similar vertical movements to the rotary shaft 102 which carries the cap plate 100, thus determining the compression of springs 98 and consequently the pressure with which upper ring 85 is forced against the balls 53. I

This adjustment may be made at any time from outside of the mill housing, without stopping the operation of the mill.

The general operation of this form of mill is much the same as that of the mill first deand is provided with an adjusting hand wheel the proper directions, the

scribed. The rotary plows 72 will project the unpulverized material upwardly from the bottom of the mill, this material being divided by the deflecting flange 87 and part of the material passing between the grinding elements and part passing upwardly through the passages 86 in the upper grinding ring 85. The inner ring 85 can yield upwardly against its own weight and the pressure of springs 98 inorder. to permit the balls to ride over foreign bodies without damage to the mill parts. The outer grinding ring 83 is not cupped upwardly sufiicient to permit the accumulation of material on the ball race, and this form of mill will be self cleaning as in the first described form of the invention.

While this improved mill has been shown n Fig. 1, and described, as used for delivermg the'material to a receptacle or storage ing, a vertical ing confined between the 5 direct to a furn ce in, suspenslon in the airstream, such sy ems being well-known in connection with other types of mills.

I claim:

1. In a planetary ball mill, a closed housshaft rotatably mounted therein, means for rotating said shaft,

ing rings centered about the shaft, the balls being confined betweengtherings, said rings including an outer ring fixed within the housing, connectin means for rotating another of the rings rom the shaft, suchconnectin'g means embodying relatively movable parts wherebythis' ring is ermitted limited lateral movements, means or yieldingly holding the latter rin in engagement with the balls, means for feeding material by gravity between thegrinding elements, means for creating an upward flow of air through the housing to carry away pulverized material in suspension, and means for mechanically projecting unpulverized material from e lower portion of the housing upwardly to the grinding elements.

2. In a planetary ball mill, a closed housing, a vertical shaft rotatably mounted therein, means for rotating said shaft, grinding elements comprising an annular series of grinding balls, and a plurality of grinding rings centered about the shaft, the balls being confined between the rings, said rings including an outer ring fixed within the housing, connecting means for rotating another of the rings from the shaft, such gconnecting. means embodying relatively movable parts whereby this ring is permitted limited lateral movements, means for yieldingly holding the latter ring in engagement with the balls,

means for feeding material by gravity between the grinding elements, means for creating an upward flow of air through the housing tocarry away pulverized material in suspension, and means carried by the rotatable shaft for mechanically feeding unpulverized material from the lower portion of the housing upwardly to the grinding elements.

3. In a planetary ball mill, a closed housa vertical shaft rotatably mounted there in, means for rotating said .shaft, grinding elements comprising an annular series 0 grinding balls, and a plurality of rinding rings centered about the shaft, the alls berings, said rings including an outer ring fixed within the housing, connecting means for rotating another of the rings from the shaft, such connecting means embodying relatively movable parts whereby this ring is permitted limited grind ing elements comprising an annular series of grinding balls, and a plurality of grindlateral movements, means for yieldingl holdi the latter ring in engagement w1tli the ba s, means for feedin material by. gravity between the grin ing elements, means for creating an upward flow of air through the housing to carry away pulverized material in suspension, and a circular series of plows carried by the rotary shaft for lifting material from the lowerportion of the housing and projecting it upwardly to the grinding elements.

4. In a planetary ball mill, a closed housing, a vertical shaft rotatably mounted there in, meansfor rotatingsaid.shaft, grinding Yelements comprising an annular series of grinding balls, and inner and outer grinding rings centered about the shaft, the balls being confined between the rings, the outer ring being fixed within the housing, connect-, ing means for rotating the inner ring from the shaft, said connecting means embodying relatively movable parts whereby this ring is permitted limited lateral movements,

spring means for yieldingly holding the latter ring in engagement with the balls, means operable from outside the housing for adjusting the tension of the spring means, and means carried by the rotary shaft for mechanically projecting material from the lower portion of the housing upwardly to the grinding elements.

5. In a planetary ball mill, a closed housing, avertical shaft rotatably mounted therein, means for rotating said shaft, grinding elements comprising. an annular series of grinding balls, and inner and outer grinding rings centered about the shaft, the balls being confined between the rings, the outer ring being fixed within the housing, connecting means for rotating the inner ring from the shaft, said connecting means embodying relatively movable parts whereby this ring is permitted limited lateral movements,

spring means for yieldingly holding the latter ring in engagement with the balls, means operable from outside the housing for adjusting the tension of the spring means, there being a" plurality of passages through the inner ringvbetween its ball engaging surface and the shaft, and a plurality of plows carriedby the shaft and adapted to lift material from the lower portion of the housing and project it upwardly, the inner ring being formed with a downwardly tapering annular wedge surface adapted to deflect the material thrown upwardlyby the plows so f that part will be directed between the balls and rings and part through the passages in the inner ring into thespaoe above the grinding elemen a 6. In a planetary ball mill, a closed housing, a vertical shaft rotatably mounted therein, means for rotating said shaft, grinding elements comprising an annular series of grinding balls, and inner and outer grinding rings centered about the shaft, the balls being confined between the rings, the outer ring being fixed within the housing, connect ing means for rotating the inner ring from the shaft, said connecting means embodying relatively movable parts whereby this ring is permitted limited lateral movements, spring means for yieldingly holding the latter ring in engagement with theballs, means operable from outside the housing for adjusting the tension of the spring means, there being a plurality of passages through the inner ring between its ball engaging surface and the shaft, and a plurality of plows carriedby the shaft and adapted to lift material from the lower portion ofthe housing and project it upwardly, partly between the grinding elements and partly through the passages in the inner ring.

7. In a planetary ball mill, a closed hous ing, a vertical shaft rotatably mounted therein, means for rotating the shaft, grinding elements comprising an annular series of grinding balls and a plurality of grinding rings centered about the shaft, said rings including an outer ring fixed within the housing, and a pairof inner rings which are adapted to engage the upper and lower portions respectively of the inner sides of the balls and force the balls outwardly into engagement with the fixed ring, means for urging the inner rings toward one another and into clamping engagement with the balls, and connecting means for rotating the inner rings from the shaft, said connecting means embodying relatively movable parts to permit limited lateral movements of the inner rings.

8. In a planetary ball mill, a closed housing, a vertical shaft rotatably mounted therein, means for rotating the shaft, grinding 7 elements comprising an annular series of grinding balls and a plurality of grinding rings centered about the shaft, said rings including an outer ring fixed within the housing, and a pairof inner rings which are adapted to engage the upper and lower portions respectively of the inner sides of the balls and force the balls outwardly into engagement with the fixed ring, spring means for yieldingly urging the inner rings toward one another and into clamping engagement with the balls, and connecting means for rotating the inner rings from the shaft, said connecting means embodying relatively movable parts to permit limited lateral movements of the inner rings.

9. In a planetarv ball mill, a closed housing, a vertical shaft rotatably mounted therein, means for rotating the shaft, grinding elements comprising an annular series of grinding balls and a plurality of grinding rings centered about the shaft, said rings including an outer ring fixed within the housing, and a pair of inner rings which are adapted to engage the upper and lower p01- tions respectively of the inner sides of the balls and force the balls outwardly into engagement with the fixed ring, spring means for yieldingly urging the inner rings toward one another and into clamping engagement with the balls, connecting means for rotating the inner rin s from the shaft, said connecting means em odying relatively movable parts to permit limited lateral movements of the inner rings, and means carried by the rotary shaft for mechanically projecting material from the lower portion of the housing upwardly to the grinding elements.

10. In a planetary ball mill, a closed housing, a vertical shaft rotatably mounted therein, means for rotating the shaft, grindin elements comprising an annular series 0 grinding balls and a plurality of grinding rings centered about the shaft, said rings including an outer ring fixed within the housing, and a pair of inner rings which are adapted to engage the upper and lower portions respectively of the inner sides of the balls and force the balls outwardly into engagement with the fixed ring, spring means for yieldingly urging the inner rings toward one another and into clamping engagement with the balls, connecting means for rotating the inner rings from the shaft, said connecting means embodying relatively movable parts to permit limited lateral movements of the inner rings, and a circular series of plows carried by the rotary shaftfor lifting material from the lower portion of the housing and projecting it upwardly to the grinding elements.

11. In a planetary ball mill, a closed housing, a vertical shaft rotatably mounted therein, means for rotating the shaft, grinding elements comprising an annular series of grinding balls and a plurality of grinding rin s centered about the shaft, said rings inclu ing an outer ring fixed within the housing, and a pair of inner rings which are adapted to engage the upper and lower portions respectively of the inner sides of the balls and force the balls outwardly into engagement with the fixed ring, spring means for yieldingly urging the inner rings toward one another and into clamping engagement with the balls, connecting means for rotating the inner rings from the shaft, said connecting means embodying relatively movable parts to permit limited lateral movements of the inner rings, there being inner passages formed in the inner rings between the ball engaging faces thereof and the central shaft, and a circular series of plows carried by the rotary shaft for lifting material from the lower portion of the housing and projecting it upwardly, the lower inner ring being formed with a downwardly tapering annular wedge surface adapted to deflect the material projected upwardly by the plows so that part will be directed between the balls and rings and part through the passages in the inner'rings. Y

12. In a planetary ballmill, a closed housing, a vertical shaft rotatably mounted therein, means for rotating the shaft, grinding elements comprising an annular series of grinding balls and a plurality of grinding rings centered about the shaft, said rings including an outer ring fixed within the housing, and a pair of inner rings which are adapted to engage the upper and lower portions respectively of the inner sides of the balls and force the balls outwardly into engagement with the fixed ring, spring means for yieldingly urging the inner rings toward one another and into clamping engagement with the halls, connecting means for rotating v the inner rings from the shaft, said connecting means embodying relatively movable parts to permit limited lateral movements of the inner rings, there being inner passages formed in the inner rings between the ball engaging faces thereof and the central shaft, and a circular series of plows carried by the rotary shaft for lifting material from the lower portion of the housing and projecting it upwardly, partly between the grinding elements and partly through the passages in the inner rings. Y

13. In a planetary ball mill, a closed housing, a vertical shaft rotatably mounted there-' in, means for rotating the shaft, grinding elements comprising an annular series of grinding balls and a plurality of grinding rings centered about the shaft, said rings including an outer ring fixed within the housing, and a pair of inner rings which are adapted to engage the upper and lower portions respectively of the inner sides of the balls and force the balls outwardly against the outer fixed ring, means for yieldingly urging the inner rings toward one another and into clamping engagement with the balls, connect-f ing means for rotating the inner rings from the shaft, said connecting means embodying relatively movable parts to permit limited lateral movements of the inner rings, means for feeding material by gravity between the grinding elements, means for creating an upward flow of air through the housing whereby pulverized material is carried away in suspension, and means carried by the rotary shaft for mechanically projecting unpulverized material from the lower portion of the housing upwardly. to the grinding elements.

14. In a planetary ball mill, a closed housing, a vertical shaft rotatably mounted therein, meansfor rotating the shaft, grinding elements comprising an annular series of grinding balls and a plurality of grinding rings centered about the shaft, said rings including an outer ring fixed within the housing, and a pair of inner rings which are adapted to engage the upper and lower portions respectively ofthe inner sides of the balls and force the balls outwardly a ainst the outer fixedring, means for yieldingly urging the inner rings toward one another and into clamping engagement with the balls,

connecting means for rotating the inner rings from the shaft, said connecting means embodying relatively movable parts to permit limited lateral movements of theinner rings, means for feeding material by gravity be tween the grinding elements, means for creating an upward flow of air throughthe housing whereby pulverized material is carried away in suspension, and a circular series of plows carried by the rotary shaft for lifting unpulverized material from the lower portion of the housing and projecting it upwardly to the grinding elements. I

15. In a planetary ball mill, aclosed housing, a vertical shaft rotatably mounted therein, means for rotating the shaft, grinding elements comprising an annular series of grinding balls and a plurality of grinding rings centered about the shaft, said rings including an outer ring fixed within the housing, and a pair of inner rings which are adapted toengage the upper and lower portions respectively of the inner sides of the balls and force the balls outwardly against the outer fixed ring, means for yieldingly tween the grinding elements, means for creating an upward flow of air through the housing whereby pulverized material is carried away in suspension, there being inner passages formed in the inner rings between the ball engaging faces thereof and the central shaft, and a circular, series of plows carried by the rotary shaft for'lifting unpulverized material from the lower portion of the hous- .1ng and projecting, it upwardly, the lower lnner ring being formed with a downwardly tapering annular wedge surface adapted to deflect the material projected upwardly by the plows so that part is directed between the balls and rings and part through the passages'in the inner rings.

16. In a planetary ball mill, a closed hous- 7 ing, a vertical shaft rotatably mounted therein, means for rotating the shaft, grindlng' elements comprising an annular series of grinding balls and a plurality of grinding rings centered about the shaft, said rings including an outer ring fixed within the housing, and a pair of inner rings which are adapted to engage the upper and lower portions respectively of the inner sides of the balls and force the balls outwardly against the outer fixed ring, means for yieldingly urging the inner rings toward one another and into clamping engagement with the balls, connecting means for rotating the inner rings from the shaft, said connecting means embodying relatively movable parts to permit limited lateral movements of the inner rings, means for feeding material by gravity between the grinding elements, means for creating an upward flow of air'through m the housing whereby pulverized material is carried away in suspension, there being inner passages formed in the inner rings between the ball engaging faces thereof and the central shaft, and a circular series of plows carried by the rotary shaft for lifting unpulverized material from the lower portion of the housing and projecting it upwardly,

partly between the grinding elements and partly through the passages in the inner o rin s.

lateral movements,

JOE CRITES.

1 In a planetary ball mill, a closed housing, a vertical shaft rotatably mounted therein, means for rotating the shaft, grinding elements comprising an annular series of grinding balls and a plurality of grinding rings centered about the shaft, said rings including an outer ring fixed within the housing, and a pair of inner rings which are adapted to engage the upper and lower porac tions respectively of the inner sides of the balls and force theiballs outwardly against the outer fixed ring, means for yieldingly urging the inner rings toward one another and into clamping engagement with the balls, 3!! connecting means for rotating the inner rings from the shaft, said connecting means embodying relatively movable parts to permit limited lateral movements of the inner rings, means for feeding material by gravity between the grinding elements, means for creating an upward flow of air through the housing whereby pulverized material is carried away in suspension, there being inner passages formed in theinner rings between the ball engaging faces thereof and the central shaft, and a circular series of plows carried by the rotary shaft for lifting unpulverized material fromthe lower portion of the housing and projecting it upwardly, partly between the grinding elements and partly through the passages in the inner rings, there being scoops on the lower ring to cooperate with the plows in projecting material upwardly through the passages in the rings.

18. In a planetary ball mill, a closed housing, a vertical shaft rotatably mounted therein, means for rotating the shaft, grinding elements comprising a series of balls adapted to travel in a horizontally disposed annular path, a plurality of grinding rings centered about the shaft between which the balls are confined, said rings including an outer ring fixed within the housing, and a pair of inner 65 rings which are adapted to engage the inner 

